Te02 mode suppressor for te01 mode circular waveguide



Nqv. 21, 1961 Ila W. K. KAHN 3,010,088 TE MODE SUPPRESSOR FOR TE MODE CIRCULAR WAVEGUIDE Filed Nov. 15, 1960 INVENTOR WALTER K. KAHN ATTORNEYS United States Patent 3,010,088 TE .MDE SUPPRESSOR FOR TE MODE CIRCULAR WAVEGUIDE Walter K. Kahn, Brooklyn, N.Y., assignor to Polytechnic Institute of Brooklyn, Brooklyn, N.Y., a corporation of New York Filed Nov. 15, 1960, Ser. No. 69,481 6 Claims. (Cl. 333-98) This invention relates to mode suppressors and more particularly to a mode suppressor for use in conjunction with a circular waveguide operated in the dominant circular TE mode. The T13 mode is suppressed by use of the present invention. The basic problem to be solved in connection with mode suppressors for circular waveguides is a suppressor for undesired modes which will not interfere with the transmission of the dominant TE mode.

Accordingly, it is the principal object of the present invention to provide a mode suppressor for the TE mode for a circular waveguide operated in the dominant TE mode which suppressor will not interfere with transmission of the dominant mode.

A further object is to provide a mode suppressor which is contained entirely within the main waveguide. Other objects and advantages will be apparent from the following detailed description when read in conjunction with the attached drawing in which:

FIG. 1 is a longitudinal sectional view of a linear halfportion of a preferred embodiment of the present mode filter as seen along the plane 1-1 of FIG. 2;

FIG. 2 is a section on the lines A-A of FIG. 1;

FIG. 3 is a section on the lines BB of FIG. 1; and

FIG. 4 is a section on the lines CC of FIG. '1.

In general, the objects of the present invention are achieved by providing within the main waveguide a plurality of smaller waveguides, each coupled to the undesired mode in the main guide and each provided with energy absorbing material for absorbing the undesired mode.

Referring now to FIG. 1, the mode filter is formed in a section of a circular waveguide having coupling flanges at the ends, only half of the section being shown. Positioned within the main guide 10 are a plurality of smaller guides 10a. These smaller guides are formed by a plurality of radially arranged metallic vane members 11 extending between the axis of the main guide and the inner periphery thereof. As shown most clearly in FIG. 4, each vane is in cross-section, a small sector of a circle, the circle being a cross-section of the main guide. As further shown in FIG. 4, each vane is solid from the axis of the main guide to a point substantially half the radial length of each vane. The remaining portion of the vane is hollow and thus defines a small waveguide 10a. From a comparison of FIGS. 2, 3 and 4, it will be apparent that each vane is longitudinally tapered over the end portions 11a to a feather or very fine edge at the end of the suppressor structure. As shown most clearly in FIGS. 1 and 3, each of the small guides includes a series of openings 12 which serve to couple the energy of the undesired mode from the main guide to each of the smaller guides. Preferably these openings are elliptical and oriented so that the major axis of the ellipse is parallel to the longitudinal axis of the main guide.

Positioned within each of the small guides and at the opposite ends of each is a small body of lossy material 13, as for example a resistance card, and this material serves to absorb the undesired mode energy carried by the small guides. The end portion of the small guides beyond the lossy material may be solid, or if hollow then the lossy material is preferably extended to fill the entire end portion.

It will be apparent to those skilled in the art that the attached sheet of drawings illustrates only one half of the mode suppressor, and further that the half not illustrated is the same shape and configuration so that both halves are symmetrical and only one half hasbeen illustrated.

As a concrete example of the relative dimensions of the suppressor and the main guide, FIG. 4 indicates that the radius of the main guide is of a dimension a,'that the radius of the locus of the coupling openings 12 has a radial dimension r, and that the radial dimension of the solid portion of each vane (inner radius of small guide) is designated by the reference [2.

The inner radius b of the small guide is so chosen that the electromagnetic field configuration within the guide is identical to the TE mode in a circular guide of radius r. For this to be so, the inner radius a must satisfy the equation where X' and X are, respectively, the first and second non-vanishing roots of the derivative of the 0th order Bessel function of the first kind. The Bessel function of the first kind is denoted by J and its first derivative by J' thus b=a(X' /X' )=(3.832/7.016)a The radius r of the coupling openings is such that at that point the H component of the TE mode in the main guide is zero. Under this condition, the following equation must be satisfied:

'Ihe dimension L of FIG. 1 may be defined as follows:

where is the coupling per unit length which may be defined as a fraction of circuit quantity (voltage or current) induced in an element of length of second line by the presence of the quantity in the corresponding element of a first line. As such it is well understood as a fundamental term.

From the foregoing it will be apparent to those skilled in the art that there is herein shown and described a new and useful mode suppressor structure for suppressing the TE mode in a circular guide driven in the dominant TE mode.

While a preferred embodiment has been herein shown and described, applicant claims the benefit of a full range of equivalents within the scope of the appended claims.

I claim:

1. A TE mode suppressor for a TE circular waveguide comprising in combination with a section of a circular wave guide: a plurality of metallic, radially arranged vanes in said guide, each such vane in cross-section comprising a sector of the circular cross-section of the guide and being solid at the inner radial portion and hollow at the outer radial portion thereof, each vane thus defining a separate small waveguide bounded at its outer periphery by the inner wall of the main guide, on its sides by the two walls of the vane and at its inner radial end by the solid portion of the vane; means defining a plurality of coupling openings, longitudinally distributed along each vane and serving to couple TE energy from the main guide to the smaller guide, said openings being positioned radially of the main guide at a point where the H component of the TE mode is zero; and means positioned within each small guide at each end thereof for absorbing energy therefrom.

2. A mode suppressor as defined by claim 1 in which each vane is longitudinally tapered to a fine edge at each end thereof.

3. A mode suppressor as defined by claim 1 in which the solid portion of the vanes extends radially from the axis of the main guide to a point approximately one-half of the radius of the main guide.

4. A mode suppressor as defined by claim 1 in which the radial location of said coupling openings is approximately two-thirds of the radius of the main guide.

a 5. A TE mode suppressor for a TE circular waveguide comprising in combination with a section of the main guide: a plurality'of metallic vanes extending radially outwardly from the axis of said main guide into contact with the inner wall'thereot, each vane in crosssection comprising a small sector of the circle defined by the cross-section of the main guide, each such vane being solid from the axis of the main guide radially outwandly to a point approximately onehalf the radius of the main guide and hollow for the remainder of its radial extent, and each vane being longitudinally tapered at each end to a feather edge, the hollow portions of each vane thus defining a plurality of small wave glides within the main guide; means defining a plurality of longitudinally distributed elliptical openings in one wall of the hollow portion of each vane, the major axis of said openings extending parallel to the longitudinal axis of said main guide, said openings serving to couple TE energy from the main guide to the smaller guides and being located approximately at a point radially of the main guide axis when the H component of the TE mode is zero; and lossy material positioned at each end of and Within each small guide to absorb the TE energy therein.

6. A mode filter for transmitting the TE mode in a circular waveguide while attenuating the TE mode comprising, in combination, a section of circular waveguide having a plurality of sector-shaped metallic vanes extending longitudinally within said section and equally spaced angularly about the axis of said section, the outer portion of each vane adjacent the wall of said circular section being hollow and forming a smaller waveguide for the transmission of the TE mode, each smaller waveguide being coupled to the space between adjacent vanes by a narrow slot formed in at least one wall of the hollow portion of each vane and extending longitudinally of said circular section, said coupling slots being located radially from the axis of circular waveguide at a point where the radial currents of the TE mode are zero, and means located in the ends of each smaller waveguide for absorbing the energy of the TE mode.

References Cited in the file of this patent UNITED STATES PATENTS Miller Aug. 19, 1958 Felsen et al Dec. 9, 1958 

